Powder bed design

I have built my first SLS prototype and are using sand as powder. However I ran in to problems with sand jamming the moving powder bed preventing a smooth motion. The friction from the powder stuck between the moving bed and the side walls makes small layer heights impossible since sometimes the bed does not even move and after some layers it suddenly jumps. Is the solution to make the gap (currently 0.1-0.2mm) even smaller? Making it lager could also maybe solve the issue but a lot of powder would fall down in between to the bottom of the printer. I also consider some type of seal but I am not sure how that could be implemented and wear would be a problem. The bed and side walls are made of 3mm aluminium and I do not know if some other material is better? If someone has had similar issues or know of a good working design I would really appreciate some advise.